1. Field of the Invention
The present invention relates to a motor driving apparatus for a power window, power seat, etc. which are mounted on a passenger car or the like and, more particularly, to an apparatus for detecting motor problems such as lock-up, short circuit, and open circuit, and a selective driving mechanism for the motor.
2. Description of the Related Art
In recent years, more passenger cars and the like are equipped with a power window, which enables a passenger to open and close the window by operating a switch, a power seat, which enables a passenger to adjust the position of the seat or the angle of a seat back by operating a switch, and other similar on-car apparatuses. Such a power window, power seat, and other similar on-car apparatuses employ motors which use the voltage from batteries mounted on passenger cars as their line voltage, the motors being driven to open and close the windows, move the seats, or operate other on-car apparatuses.
The on-car apparatuses stated above are provided with self-diagnosing devices which detect motor failures such as lock-up, open circuit, and short circuit and stop the motors so as to clear such failures.
FIG. 9 is a circuit diagram illustrative of an embodiment of such an on-car motor driving apparatus. The apparatus is equipped with a motor 131, a selector switch 132 which has a moving contact terminal 132b, and fixed contact terminals 132a, 132c, a selector switch 133 which has a moving contact terminal 133b and fixed contact terminals 133a, 133c, a current value detecting resistor 136, a differential amplifier 137, and a microprocessor unit (MPU) 138 provided with an analog-to-digital converter (A/D converter).
The selector switches 132 and 133 are connected to the output side of the MPU 138 via a first inverter 134 and a second inverter 135, respectively; they are connected to the MPU 138 also via the differential amplifier 137 which detects the voltage across the two terminals of the current value detecting resistor 136. An operating switch 139 is provided for controlling the direction in which a moving unit moves and it is connected to the MPU 138. The current flowing through the motor 131 also flows through the current value detecting resistor 136 which is connected in series with the motor 131. The selector switches 132 and 133 are energized by a driving output of the MPU 138 which is supplied via the first inverter 134 and the second inverter 135, respectively. The terminal voltage of the current value detecting resistor 136 is detected by the differential amplifier 137 and the detected terminal voltage is supplied to the MPU 138.
The following description gives an outline of the on-car motor driving apparatus having the construction stated above.
In the drawing, if both selector switches 132 and 133 are set down in FIG. 9, i.e. if they are closed to make contact between 132b and 132c and between 133b and 133c, then the two terminals of the motor 131 are short-circuited via the selector switches 132, 133, and no power is supplied to the motor 131 which, therefore, stays in a stationary state. Hence, a moving unit such as the window does not move at all.
If the moving contact of the selector switch 132 is moved up in FIG. 9 to make contact between the moving contact terminal 132b and the fixed terminal 132a, with the selector switch 133 closed to make contact between terminals 133b and 133c, then a current path is formed from a power terminal 140, through the moving contact of the selector switch 132, the motor 131, the moving contact of the selector switch 133, and the current value detecting resistor 136 to ground. This lets current flow into the motor 131, causing the motor to rotate in the forward direction. As a result, a moving unit such as the window is opened.
If the selector switch 133 is set up in the drawing to make contact between the moving contact terminal 133b and the fixed contact terminal 133a, with the selector switch 132 kept in the down position in the drawing, that is, with the moving contact terminal 132b and the fixed contact terminal 132c kept in contact, then a current path is formed which leads from a power terminal 140, through the moving contact of the selector switch 133, the motor 131, the moving contact of the selector switch 132, and the current value detecting resistor 136 to ground. This lets current, flowing in the opposite direction from that in the preceding case, to pass through the motor 131, causing the motor to rotate in the reverse direction. Thus, a moving unit such as the window is closed. The selector switches 132 and 133 are controlled by the MPU 138 in accordance with the state of the switch 139 which is controlled by a passenger.
Whether the motor runs in the forward or reverse direction, the motor current flows through the current value detecting resistor 136, generating a voltage which corresponds to the motor current. The generated voltage is amplified by the differential amplifier 137 which is constituted by an operational amplifier. The output voltage of the differential amplifier 137 is sent to the MPU 138, then it is converted to a digital value through the A/D converter. Based on the digital value, the MPU 138 determines whether the motor 131 has incurred a failure or not. If the result of the determination indicates a problem with the motor, the MPU 138 sets down the selector switches 132 and 133 to stop the motor 131.
The on-car motor driving apparatus constructed as described above is designed so as to be able to detect an object that is caught at the window while the window is being closed.
More specifically, as illustrated in FIG. 10A illustrative of the changes in motor current I, when the moment the motor 131 is started, an inrush current is produced, causing motor current I to rapidly rise and then rapidly fall. When the motor 131 reaches a steady state and the inrush current ends, a low steady-state value is generated. When the window is completely closed and no longer makes any movement, motor current I suddenly increases.
In the motor driving apparatus shown in FIG. 9, the MPU 138 sequentially captures the digital value data which is obtained by subjecting the outputs of the differential amplifier 137 to the A/D converter, then it determines the rate of change .DELTA.I/.DELTA.t of the motor current from a difference .DELTA.I between the digital values of two pieces of data which have been captured in succession. The MPU 138 then determines that the motor 131 has locked if the result of comparison of the rate of change with a preset positive value K' is as shown below and it sets down the selector switches 132 and 133 to stop the motor: EQU .DELTA.I/.DELTA.t&gt;K'
Thus, when the window is closed and the motor 131 is no longer allowed to rotate, motor current I suddenly increases as indicated by the solid line in FIG. 10A. This sudden rise can be detected and the motor 131 can be stopped. The motor current suddenly increases as indicated by the solid line shown in FIG. 10A also when the window locks in the middle of closing due to something caught at the window, preventing the motor 131 from continuing its rotation. This, therefore, can also be detected and the motor 131 can be stopped.
A motor employed for an on-car apparatus such as a power window and power seat is equipped with two selector switches whereby switching between the forward rotation and the reverse rotation can be accomplished as described with reference to FIG. 9. FIG. 11 shows an example of a motor selective driving mechanism employed when two motors are involved. The motor selective driving mechanism is provided with motors 101a and 101b and selector switches 102a, 102b, 103a, and 103b.
In the drawing, the same connection as that shown in FIG. 9 applies to the connection between the selector switches 102a, 102b, 103a, and 103b, the power supply, and the grounding terminal, the self-diagnosing device composed primarily of the resistor 136 shown in FIG. 9 being omitted in this example. This construction allows the motor 101a to run in the forward or reverse direction or to be stopped by changing the setting of the selector switches 102a and 103a. In the same manner, the motor 101b can be rotated in the forward or reverse direction or it can be stopped by changing the setting of the selector switches.
FIG. 10 gives characteristic plots illustrative of the operating characteristics of the known on-car motor driving apparatus. FIG. 10A shows the changes in the current flowing through the motor 131; FIG. 10B shows the changes in the lock current when the driving voltage of the motor 131 fluctuates. In FIGS. 10A and 10B, the axis of ordinate indicates the motor current; the axis of abscissa indicates time.
The current flowing through the motor 131 exhibits the changes as shown in FIG. 10A: the current value temporarily increases because of the large inrush current coming in during the period from time t0 to time t1 which is the starting period of the movement of a moving unit such as a window. After time t1, the revolution of the motor 131 reaches the stable state and a normal current of an approximately constant value flows. When the revolution of the motor 131 is prevented because of an object having been caught at a moving unit, e.g. a window, or because of the window having reached the moving end position in time t2, a lock current, which increases within unit time .DELTA.t (t2.about.t3) begins to flow. Reference character Vb denotes the voltage which is directly supplied from a car battery; its voltage value may slightly change due to an external environmental factor or it may decrease as time elapses in the course of a prolonged use. In this case, as shown in FIG. 10B, the lock current increases according to the driving voltage of the motor 131, i.e. voltage Vb supplied to the power terminal 140; the increasing curve grows steeper as driving voltage Vb increases.
In the known on-car motor driving apparatus, as shown in FIG. 10B, unit time .DELTA.t for detecting current variation .DELTA.i is fixed; therefore, current variation .DELTA.i per unit time .DELTA.t significantly varies when driving voltage Vb of the motor 131 fluctuates. Hence, current variation .DELTA.i per unit time .DELTA.t markedly varies with respect to any driving voltage Vb within the variation range. Accordingly, the known on-car motor driving apparatus is designed to permit the detection of current variation .DELTA.i per unit time .DELTA.t on any driving voltage Vb in the variation range, and therefore, a fixed value is provided as preset value .DELTA.is which corresponds to current variation .DELTA.imin per unit time .DELTA.t obtained from minimum driving voltage Vbmin. With such preset value .DELTA.is selected, however, a large motor torque results if an object is caught in a moving unit when maximum driving voltage Vbmax or driving voltage Vb close to the maximum driving voltage is being applied and the motor to be overloaded. This calls for an emergency stop of the motor to prevent the caught object from being damaged. For this reason, the circuit tends to become complicated.
Further, in the on-car motor driving apparatus illustrated in FIG. 9, whether the motor 131 is running or not, power is constantly supplied from the battery to the power supply terminals of the operational amplifier constituting the differential amplifier 137. Hence, the self-diagnosing device of the on-car motor driving apparatus constantly consumes power. The power window or power seat, however, is not used very often; therefore, the constant supply of power to the self-diagnosing device results in the wasteful consumption of a vast amount of power. This presents a serious problem especially when a battery provides the power source.
Furthermore, as shown in FIG. 10A, the on-car motor driving apparatus enables the detection of a failure in the middle of the operation of the power window or power seat. If the apparatus were designed to determine that a failure has occurred whenever the comparison result indicates .DELTA.I/.DELTA.t&gt;K' as described above, then the following problem would arise: motor current I at the time of start of the motor 131 rapidly increases because it develops an inrush current as shown in FIG. 10A, and since the rate of variation .DELTA.I/.DELTA.t of motor current I at that time would satisfy the expression given above, the MPU would determine that a failure has occurred and consequently stop the motor 131. As a result, the opening or closing of the power window, for example, would be interrupted.
To avoid the problem mentioned above, the known self-diagnosing device is designed not to detect a failure of the motor 131 during inrush current generating period T (e.g. 100 msec) before motor current I reaches the steady-state current since the start-up of the motor 131. This, however, gives rise to the following inconvenience: in the case of a power window, for example, when the motor 131 is actuated to close the window, which has been closed halfway, with something stuck in the window, the motor 131 is allowed to run only for a short time period before it is brought to a stop. Therefore, the rising motor current I due to the failure overlaps the inrush current at the time of the start-up, making it impossible detect the failure because it happens during the period when the inrush current takes place.
Furthermore, in the selective driving mechanism of the on-car motor driving apparatus shown in FIG. 11, each motor requires two selector switches. Hence, as the number of motors increases, the required number of selector switches increases accordingly. The selector switches are costly relay switches which are controlled by a microprocessor unit. An increase in the number of required selector switches therefore adds greatly to the price of the power window, power seat or other car-mounted apparatus.